Asked by a caller to a local news television programme whether he knew how much state pensioners received, he tried to dodge the question, before finally mumbling: "I think it's about £30 quid now, isn't it?"

In fact, the basic pension is £90.70 a week for a single person and £145.45 for a couple, with more available for those claiming tax credits.

Mr Clegg's error, during an interview with ITV Westcountry, threatens to overshadow his keynote speech which will close the Liberal Democrat conference.

He was speaking in response to a question from viewer Wally Cotgrave, a retired blacksmith from Sidmouth, Devon, 69, who afterwards said he was unimpressed with Mr Clegg's answer.

Mr Cotgrave, who himself claims the state pension with his wife Maureen, 73, added: "People like him make the right noises and say the right things when they want your vote, but they don't actually know anything. They're all out of touch.